1993 Mustang LX 4 cylinder running rough

A few months ago I bought a 1993 Mustang Hatchback 4 cylinder N/A, with the automatic transmission. The problem I'm having is that the car doesn't run quite right. At low speeds(40 and below), and low rpms, the exhaust smells very gassy, and I get very poor mileage in low speed stop and go traffic. Also, when I come to a stop the engine occasionally shudders, like it's going to stall out. And when slowing down from the engine pops, like it's backfiring. I've replaced all the usual stuff, the spark plugs, the air filter(with a K&N), pcv valve, transmission fluid/filter and the fuel filter.
Anyone have any ideas what to look at for improving the car's mileage/performance?

I just pulled the codes from the car. The only one I get is during the Key On Engine Off test: Code 629 - converter clutch solenoid circuit fault or lock up solenoid circuit fault. No other codes were present.
However, I haven't found an explanation of this code, nor do I know it's related. Seems possible that a transmission problem would make the car run so strangely, but I don't know.
Anyone know what this one means?

Founding Member

It could. The TCC solonoid leaving the TCC on when your comming to a stop, your still in high gear, therefore the rpm's go low like an manual left in a high gear at slow speed, so the IAC opens up to try to correct the rpm causing low vaccume, making it studder and pop. Just a possibility. I can't see the car in person, so it's hard to dianose over the net.

The backfiring comes out the exhuast as popping noise.
Also, I check the EGR and it seemed to be functioning normally.
I plan to replace the Fuel Pressure Regulator and the Converter solenoid this weekend.

I have an 87 LX 4-banger. One day it had no power and the fuel economy dropped from about 30 to 20mpg. Long story short... the timing belt had jumped a tooth. I bought a new one put it on, and the car runs great. My problems sound similar to yours, but I am not sure what the differences between and 87 and a 93 will be.
It should be easy to check via the plug in the front of the timing cover.

Yeah, I have almost the same problem, except mine does stall out. 1993 4 cyl dual spark, already replaced the ICM cause my tach died and IF it ran, I got a couple miles before it died, and now it's down to the MAF, TPS, CKS and fuel pump. Regulator is good, unknown fuel pressure, and the manifold pressure is good. No engine code, no backfiring really, just shudders hard and dies. My repair guide says check ignition timing, EGR, fuel system, and manifold vacuum so there's a few good places to start.

Just a note about my experiance with my 90 LX. When I bought the car, it ran very rough after running about 3 minutes. A shop had diagnosed #3 cylinder as being dead and were trying to sell the owner a rebuild. I played with it for days before swapping the motor. Started it up, and SAME problem. I never did find it, but to bypass it, I wired the #2 & #3 injector feeds together. HUH!, you might say. Turns out these cars fire TWICE per cycle AND fire in banks. While one is firing on compression, the other is firing on exhaust. The running rough and poor milage was because the #3 injector was STAYING OPEN all the time the car was running. After the re-wiring, the problem went away. Runs good still today and gets 30-32 mpg on the highway.

i had these symptoms
- check eng light would come on if i went past 2500 rpm in any gear (with no performance change)

- slight stumble at idle plus sub par acceleration

- just recently a stalling condition at idle with trouble getting the engine restarted + some black smoke coming out of exhaust

Between the stalling and the black smoke i began to think fuel system so...

I dumped the tank because the last thing i did before the first stall was fill up (i was thinking i had bad gas) i put new premium gas in with no effect. So, I checked for pressure at the fuel pump, checked for a leaking regulator and checked for a restricted fuel filter but found nothing. Having 2 plugs per cylinder i really didnt think it was ignition related but i checked anyways and found everything to be ok. I knew i had fuel air and spark which could only mean a bad sensor or module somewhere (possibly the BAP, MAF or ignition module) which seems to be where most of you are stuck.

that what it sounds like what my stang is doin i have a 89 2.3 5spd it dies when i start it up in the morning and it backfires when the engine starts to warm up and the car lunges in 3rd and 4th and 5th gear and sumtimes 1st and 2nd